1. Field of the Invention
The present invention relates to a video signal recording apparatus that records a compressed and encoded video signal on a recording medium.
2. Description of the Related Art
In recent years, camera-integrated video tape recorders (VTRs) that can record and reproduce high definition (HD) video signals have been commercially produced. The HD camera-integrated VTR has adopted MPEG (Moving Pictures Experts Group)-2 as a compression and encoding technique for a video signal. Then, compressed and encoded bit streams are recorded on a magnetic tape in a recording format in which an error correction code generation unit (also referred to as an ECC unit) is used as a minimum unit of recording.
A conventional technique for the seamless recording of data recorded on a magnetic tape is known. When re-recording new data on a recorded tape is performed, since error correction code is generated in the minimum unit of recording, re-recording is performed after reproducing data from the recorded tape and detecting the minimum unit of recording including a frame switching point (Japanese Patent Application Laid-Open No. 2000-134568).
According to the above conventional technique, a frame switching point within the minimum unit of recording reproduced from the recorded tape is detected and then new data is re-recorded from the frame switching point. However, a structure of the above conventional technique shows that only a frame switching point is detected and neither information indicating a field of a first frame in display order at the frame switching point nor information indicating presence/absence of any redundant repeat field is referenced. This can cause such problems (1) and (2) as shown below:
If data recorded on a magnetic tape is 24 frames progressive (24p) video,
(1): fields of the same kind may appear successively depending on a frames for connection, thus resulting in a field order error, and
(2): decoding time, which normally does not occur, may occur at an editing point.
The aforementioned problems will now be described in detail below. FIG. 2 shows a state when a 24p video signal is recorded on a magnetic tape and also a state when a 60 fields interlace (60i) or 30 frames progressive (30p) video signal is recorded on a magnetic tape.
Here, since film footage transmits 24 frames/second while a video signal (NTSC system) recorded on a magnetic tape transmits 30 frames/second (60 fields/second), field number conversion is performed for a 24p recording by a 2-3 pull down.
The 2-3 pull down is a technique, as shown concretely in FIG. 3, that performs the 24p field number conversion by inserting a redundant repeat field (repeat field) for every other frame. The video signal obtained by performing the 2-3 pull down is characterized in that a frame beginning with a top field and a frame beginning with a bottom field appear alternately for every two frames because a repeat field is inserted for every other frame.
When a normal 60i or 30p video signal is recorded, as shown in FIG. 2, all frames begin with a top field because two continuous fields beginning with a top field are normally encoded as a frame.
Therefore, when an MPEG-encoded 60i video signal is newly recorded on a tape on which a video signal subjected to the 2-3 pull down and MPEG encoding was recorded, a field order error in which top fields appear successively may occur depending on a frame position for connection. FIGS. 4A and 4B show examples in which a field order error occurs, and FIGS. 5A and 5B show the details thereof. In these cases, such a frame position is inappropriate as an editing point for a seamless recording.
In addition, since there is no specification regarding the repeat field, in an example shown in FIG. 4C, decoding time, which normally does not occur, occurs at an editing point. FIG. 6 shows an enlarged view of the example of FIG. 4C in code order. As is apparent from FIG. 6, abnormal decoding time is caused when the example of FIG. 4C is rearranged in code order.
That is, if a video signal recorded on a magnetic tape is 24p and a 60i video signal is seamlessly recorded, FIG. 4D is an only example in which a seamless recording can be made. However, the conventional technique does not provide a method for detecting an editing point where a normal seamless recording can be performed.